django: Why won't my custom widget populate with values from a database object?

Question

I wrote a custom widget for my Django application to interface Twitter Bootstrap's button groups with a select multiple widget (never liked those things). It works beautifully except for one thing: When I instance my form from a database object, the values don't get filled.

What's really puzzling is that it does populate these widgets when I create the form passing request.POST to the constructor. It seems to be a difference in either the data that comes through or the way the form is filled from the database object versus from the POST object, but I'm not sure where to go from there.

Here's the widget:

from itertools import chain
from django.forms.util import flatatt
from django.forms.widgets import CheckboxSelectMultiple
from django.utils.encoding import force_unicode
from django.utils.html import conditional_escape
from django.utils.safestring import mark_safe

# todo-devon Values are not preserved with object instances
class BootstrapButtonSelect(CheckboxSelectMultiple):

    def __init__(self, attrs=None, all=False, none=False, classes=[], layout='horizontal'):
        """
        Optional arguments for creating a BootstrapButtonSelect widget. Default settings are in brackets.

        all=True/[False]
        Adds a button to select all options when set to True.

        none=True[False]
        Adds a button to select none of the options when set to True.

        classes=[]
        A list of strings which adds CSS classes to the buttons making up the button select widget. The btn class is already included. Examples: 'btn-large', 'btn-primary'

        layout=['horizontal']
        Sets the layout of the button select widget to 'horizontal' or 'vertical' (Not yet implemented. All groups are currently vertical.)
        """
        super(BootstrapButtonSelect, self).__init__(attrs)
        self.all = all
        self.none = none
        self.layout = layout

        if classes:
            self.classes = u' %s' % u' '.join(classes)
        else:
            self.classes = u''


    def render(self, name, value, attrs=None, choices=()):
        """
        Builds button group and select list for widget
        """
        # todo-devon Add code for horizontal layout
        if value is None: value = []
        has_id = attrs and 'id' in attrs
        final_attrs = self.build_attrs(attrs, name=name)

        # Create the select multiple widget
        select_output = [u'<select class="button-toggles" id="%s" multiple="multiple"%s>' % (name, flatatt(final_attrs),)]
        for i, (option_value, option_label) in enumerate(chain(self.choices, choices)):
            # If an ID attribute was given, add a numeric index as a suffix,
            # so that the checkboxes don't all have the same ID attribute.
            if has_id:
                final_attrs = dict(final_attrs, id='%s_%s' % (attrs['id'], i,))
            option_value = force_unicode(option_value)
            option_label = conditional_escape(force_unicode(option_label))
            if option_value in value:
                select_output.append(u'<option value="%s" selected="selected">%s</label>' % (option_value, option_label))
            else:
                select_output.append(u'<option value="%s">%s</label>' % (option_value, option_label))
        select_output.append('</select>')
        select_output = u'\n'.join(select_output)

        # Create the button group
        button_output = [u'<div class="btn-select-vertical span3 hidden-phone" id="%s" data-toggle="buttons-checkbox">' % name]
        for i, (option_value, option_label) in enumerate(chain(self.choices, choices)):
            # If an ID attribute was given, add a numeric index as a suffix,
            # so that the checkboxes don't all have the same ID attribute.
            if has_id:
                final_attrs = dict(final_attrs, id='%s_%s' % (attrs['id'], i,))
                label_for = u' for="%s"' % final_attrs['id']
            else:
                label_for = ''
            option_value = force_unicode(option_value)
            option_label = conditional_escape(force_unicode(option_label))
            button_output.append(u'<label%s class="btn%s" id="btn-%s-%s" data-name="%s,%s">%s</label>' % (label_for, self.classes, name, option_value, name, option_value, option_label))
        button_output.append(u'</div>')
        button_output = u'\n'.join(button_output)

        # Buttons for select all or none
        if self.all or self.none:
            select_all_none_button_output = [u'<div class="btn-group all-none-buttons" data-toggle="buttons-radio" data-name="%s">' % name]
            if self.all:
                select_all_none_button_output.append(u'<button class="select-all btn%s" type="button" data-name="%s">All</button>' % (self.classes, name,))
            if self.none:
                select_all_none_button_output.append(u'<button class="select-none btn%s" type="button" data-name="%s">None</button>' % (self.classes, name,))
            select_all_none_button_output.append(u'</div>')
            select_all_none_button_output = u'\n'.join(select_all_none_button_output)

        # Full output
        if select_all_none_button_output:
            output = "%s\n%s\n%s" % (select_output, button_output, select_all_none_button_output)
        else:
            output = "%s\n%s" % (select_output, button_output)

        return mark_safe(output)

    class Media:
        js = ('/static/bootstrap-button-multiselect.js',)
        css = {
            'all': ('/static/bootstrap-button-multiselect.css',)
        }

In case you're confused, I'm using CSS to show the buttons on larger screens then swapping back in the select multiple widget on phones and tablets. My view function:

from django.http import HttpResponseRedirect
from django.shortcuts import render_to_response
from django.template.context import RequestContext
from tickets.forms import TicketForm
from tickets.models import Ticket

def addEditTicket(request, op='add', encrypted_pk=None, cipher=None):
    """
    Form and processing for new tickets
    """
    if encrypted_pk is not None:
        pk = int(encrypted_pk) ^ cipher
        ticket  = Ticket.objects.get(pk=pk)
        form = TicketForm(instance=ticket)
        initialData = {'form': form, 'form_action': '/ticket/' + op + '/', 'title': op.capitalize() + ' a ticket'}
        csrfContext = RequestContext(request, initialData)              # adds CSRF token to form context
        return render_to_response('form.html', csrfContext)             # pass context with token to form

    if request.method == 'POST':
        form = TicketForm(request.POST)
        if form.is_valid():
            new_ticket = form.save()
            form = TicketForm(instance=new_ticket)
            # todo-devon Notify user in new form that object was saved
            # Context includes form object, URL for form action (dynamically generated from argument passed as op),
            # and a title dynamically generated from operation combined with the object type in question.
            initialData = {'form': form, 'form_action': '/ticket/edit/', 'title': 'Edit a ticket'}
            csrfContext = RequestContext(request, initialData)      # adds CSRF token to form context
            return render_to_response('form.html', csrfContext)     # pass context with token to form
    else:
        form = TicketForm()

    # Context includes form object, URL for form action (dynamically generated from argument passed as op),
    # and a title dynamically generated from operation combined with the object type in question.
    initialData = {'form': form, 'form_action': '/ticket/' + op + '/', 'title': op.capitalize() + ' a ticket'}
    csrfContext = RequestContext(request, initialData)              # adds CSRF token to form context
    return render_to_response('form.html', csrfContext)             # pass context with token to form

Sorry to dump all this code in here. Thanks in advance.

EDIT: Took out the Javascript. It wasn't really relevant to the question, and I'm afraid it made my question look more daunting.

Answer 1

Found the solution, and, I'm not proud to say, I don't know why it works. I had to iterate through the selected values and force unicode on each of them. I assume the objects from the database are not in unicode. I don't understand why this would keep them from being matched and set when the widget is initialized, but I'm just glad it works. I combed through the Django default select widget to find this solution.

Thanks, everyone, for your time.